This antenna, or at least the one I made, not only covers 10-20m but tunes quite well to 40 and 80, has a reasonable swr at 6m! and a good swr from 120mhz to over 150mhz and can be used on 2m!! I was very pleasently surprised by this. Ideal for a base antenna for these multiband radios FT-100 etc.
5 Band Cobweb antenna I am building at the moment. (15/3/04). Now built. (20/3/04) Works brilliantly !. Bands covered are 2,6, 10,12,15,17,& 20. See note below Overall size is 8 ft square. Each pole is 6ft8ins. (Fishing rod blanks bought on EBAY 4 for £18.00p including postage). Total cost to date, approx. £30.00p Notice coax balun under base plate. See texts for where to get Fibre Glass Blanks.Very pleased with results.
Clamps made from saw-split ali tube.
Dont know what this bracket was from, think it was on a dish mount.
Connector made from choc block inserts removed and soldered onto component strip, each side shorted together using copper wire
Fishing rod end araldited into plastic box
The antenna will tune fairly accurately six feet from the ground and does not seem to be affected much by buildings or metalwork around it. It does though
tend to "go up" in freq when raised.
I have tested the fibre glass blanks in the microwave to check for metal content in the paint and there seems to be none. These were supplied by Les Jackson (G4HZJ) ([email protected]) Who can be found on EBAY by a search for FIBRE GLASS. They were only £18.00 for four 9 ft blanks including postage! The total cost was less than £30.00p to build and I am sure you can scrounge most of the bits.
The clamps for the poles were made by sawing through a piece of 5/8" ali pipe down the middle and tapping it out over a wider piece of pipe to fit over the fishing pole ends, drilling through them and the base plate to clamp the rods onto it.Dow Corning was used along the pipes/base to further fix them..
The antenna was set-up using an MFJ antenna analyser.
(I dont have one but our Radio Club does!)!
It is at about 22 ft and gives better results than my 6 trap 4 band dipole in the background which is 15ft higher!!
This antenna is OMNIDIRECTIONAL
So you dont need a rotator
Make sure you waterproof connector box!!
If you are unable to build this antenna and still want one, a kit of high quality, pre-tuned parts is available from the ORIGINAL DESIGNER, on his website at WWW.G3TPW.UKGATEWAY.NET
or you can contact Steve at [email protected]
I would like to take this chance to thank Steve for his advice.
I would like to point out that although this antenna will present a good VSWR on bands it is not intended for, its efficiency on these bands will be greatly reduced, but still very handy for local use!.Mine shows 1:1 on 10,12,15,17,20,2 & 70cms. 1.5 to 2.0:1 on 6m. We have just gone through a day of gale force winds here and it is still up OK! Time will tell though.
The idea for building this antenna came from a visit to me by another amateur who had just built two.The original design is by G3TPW
VSWR readings taken today(31/3/04)
Still to adjust 17m again when weather better
Other tuning points noted at 50 ohms on the MFJ analyser
144-148 Around 1.5:1
Six turns 4-6inches diameter.
You may find answers to any questions you might have published in my Guest Book